This is what seems straightforward to me.
Thought is a computation. OK.
Experiential reality is a computation. OK.

No. When you say "experiential reality" is a computation, you are
saying something ambiguous, where comp is far more precise. Because
if I can survive with a digital brain, then the experiential
reality, the first person, subjective, experience is not a
attachable to a computation, but to an infinity of computations,
and it obeys a logic driven by the knowing arithmetical points of
view, which makes it closer to the non computable notion of "inner
god" than to a 3-person computation. The first person cannot even
describe (or name, in the logician terms) itself.

Yes! As Everett demonstrates, experiential reality is essentially a
very simple computation.

?

Everett reduces it to the memory mechanism (a bit like in the first
step of the UD Argument). But this is not a computation, nor does it
explain what is experential. And it relies on a non computable notion
of "all consistent observation", which is not computable by the
observer itself.

It is the addition of each new observation to the record of
observations.

That is not computable. It might be computable with oracle.

The not so simple bit is the computation of each new observation,
though in the Everything concept it is relatively simple, since it
is simply all possible observations.

We have discussed a lot about the difficulty of the word "all", and
"possible".

If variables ψ, observation, and observables[], and function
get_sensorium_contents() were instantiated in suitably coherent
memory of a quantum computer, such a program would produce the
subjective realities of all possible functional identities of an
observer, in the form of Everett's branching tree of memory
configurations.

It should be noted that objectively, in a no-collapse universe, ψ is
properly a pointer, or reference, to a pre-existing quantum state,
and that the implementation of the statement

new_observation = compute_neural_state (ψ, t);

is simply reading a specific attribute of that quantum state, as
from a lookup table. This works very nicely given that each
observable is a correlation with a specific quantum state of the
environment, the correlations record being the simultaneity of all
such correlations: a set of commuting operators.

Simple or not, this does not seem ambiguous.

OK, very cute, but you assume ψ as oracle, and even a sort of space-
time, which is the treachery I told you about. But to understand why
it is "treachery", and why it put the (mind) body problem under the
rug, you need to study the step seven, and for this you need to
understand completely the first person indeterminacy.